1. Field of the Invention
The present invention relates to an apparatus for inspecting wires bonded between pads on a semiconductor chip and leads of a lead frame and more particularly to an illuminating device used in such an inspecting apparatus.
2. Prior Art
Japanese Patent Application Laid-Open ("Kokai") No. 3-76137 discloses one example of inspection apparatuses for bonding wires. This device inspects such wires as shown in FIGS. 5 and 6 which are bonded between pads 2 on a semiconductor chip 1 and leads 4 of a lead frame 3.
The inspection apparatus comprises as shown in FIG. 9: an inspection stand 10 for a sample 6 which has been bonded as shown in FIGS. 5 and 6; a multiple number of light bulbs 11 which illuminate the sample 6; a CCD camera 12 which images the wires 5 illuminated by the light bulbs 11 and outputs image signals; an image processing arithmetic unit 13 that processes the image signals from the CCD camera 12, recognizes the wire shapes and locates the bonding positions of the wires 5; and an X-Y table 14 that moves the CCD camera 12 around.
In this apparatus, the sample 6 is illuminated by the light bulbs 11, and the X-Y table 14 is driven so that the CCD camera 12 is positioned above the sample 6. Then, via the image processing arithmetic unit 13, the image signals of the sample 6 obtained by the CCD camera 12 are subjected to an enhancement (restoration) which includes noise elimination, emphasis of the edge area of the sample, and enlargement or reduction of the image, etc., so that the image of the sample can be seen clearly. Afterward, inspection and measurement are performed.
In the prior art apparatus as described above., however, there are limits on enhancement (restoration) of the image signals, which result in that the enhanced (restored) image differs greatly from the actual sample. In addition, the enhancement (restoration) operation usually takes time, and it is difficult to obtain reliable inspection and measurement results.
More specifically, as shown in FIGS. 5 and 6, the semiconductor chip 1 is bonded to the lead frame 3 via a paste 7 which is, for example, an epoxy resin, and the paste 7 is often squeezed out around the edges of the semiconductor chip 1. The squeezed out paste causes problems. When, for example, an inspection and measurement is made on the wire 5A by illuminating the wire 5A with the light bulbs 11, illumination from the direction A in FIG. 6 causes light, that is irregularly reflected by the paste 7, to enter the CCD camera 12. In this case, the brightness of the surface of the wire 5A and the brightness of the light that is irregularly reflected by the paste 7 are about the same; as a result, the CCD camera 12 cannot obtain a clear image of the wire 5A itself over the paste 7. Accordingly, the obtained image looks as if there is no wire 5A.
Furthermore, as shown in FIGS. 7 and 8, bonding is performed in each case with a ball part 5a, which is at the end of the wire extending out of a capillary of a bonding machine, being flattened on the corresponding pad 2. However, in the conventional illumination method, the shape (or the edges) of the bonded ball part and the shape (or the edges) of the crescent 5b of the wire 5 bonded to the lead 4 are not emphasized in the obtained image.